Method of forming resist pattern, positive resist composition, and layered product

ABSTRACT

There are provided a method of forming a resist pattern that enables the resist pattern to be formed with good control of the pattern size, as well as a positive resist composition used in the method, and a layered product formed using the positive resist composition. In the above method a positive resist composition comprising a resin component (A), which contains a structural unit (a1) derived from a (meth)acrylate ester represented by a general formula (I) shown below, and displays increased alkali solubility under action of acid, and an acid generator component (B) that generates acid on exposure is applied to a substrate, a prebake is conducted, the resist composition is selectively exposed, post exposure baking (PEB) is conducted, alkali developing is then used to form a resist pattern, and the pattern size of the thus produced resist pattern is then narrowed by heat treatment.

This application is the U.S. National Phase under 35 U.S.C. 371 ofInternational Application PCT/JP2003/015347, filed Dec. 1, 2003, whichclaims priority to Japanese Patent Application No. 2002-350353, filedDec. 2, 2002. The International Application was published under PCTArticle 21(2) in English.

TECHNICAL FIELD

The present invention relates to a method of forming a resist pattern,comprising a step for narrowing the pattern size of the resist patternby conducting a heat treatment following formation of the resistpattern, as well as a positive resist composition that is ideally suitedto use within such a method, and a layered product that uses such apositive resist composition.

BACKGROUND ART

In recent years, in the manufacture of semiconductor elements and thelike, advances in lithography techniques have lead to rapid progress inthe field of miniaturization. Typically these miniaturization techniquesinvolve shortening of the wavelength of the exposure light source. Untilrecently, ultraviolet radiation such as g-lines and i-lines have beenused as the exposure light source, but recently, KrF excimer lasers (248nm) have been introduced, and even ArF excimer lasers (193 nm) are nowstarting to be used.

Resists for use with light sources such as KrF excimer lasers and ArFexcimer lasers require a high resolution capable of reproducing apattern of minute dimensions, as well as good sensitivity relative tolight sources with this type of short wavelength. One example of a typeof known resist that satisfies these conditions is a chemicallyamplified positive type resist composition comprising a base resin thatdisplays increased alkali solubility under the action of acid, and anacid generator that generates acid on exposure (see patent reference 1)

In the reaction mechanism of a chemically amplified resist, exposurecauses the acid generator within the resist to generate acid, and thisacid causes a change in the solubility of the resin. For example, if adissolution inhibiting group that dissociates in the presence of acid isintroduced into the resin, then this dissolution inhibiting group willdissociate only within the exposed sections of the resist, causing asignificant increase in the solubility of the resist in the developingliquid within these exposed sections. Typically the dissociationreaction of the dissolution inhibiting group is accelerated byconducting a post exposure baking (PEB) treatment. Furthermore, the PEBtreatment also promotes the diffusion of acid within the resist, meaninga much higher sensitivity can be achieved than with conventionalnon-chemically amplified resists.

In KrF excimer laser lithography, polyhydroxystyrenes or derivativesthereof in which the hydroxyl groups are protected with an aciddissociable, dissolution inhibiting group, which display hightransparency relative to a KrF excimer laser (248 nm), have been used asthe base resin component of chemically amplified resists. However, theseresins display unsatisfactory transparency near 193 nm, and areessentially unusable for ArF excimer laser lithography. Accordingly,current base resins for ArF resists utilize a (meth)acrylic polymercomprising, as an acid dissociable, dissolution inhibiting group, analiphatic polycyclic hydrocarbon group with a polycyclic skeleton suchas an adamantane structure, and with a tertiary carbon atom within thisskeleton.

In recent years the degree of miniaturization has progressed rapidly,and nowadays, resolutions capable of generating line and space patternsof less than 100 nm and isolated patterns of no more than 70 nm arebeing sought. As a result, in addition to the research and developmentbeing conducted on resist materials to enable ultra-miniaturization,research is also being conducted on pattern formation methods to developtechniques capable of overcoming the resolution limits of resistmaterials.

One example of such a technique, which has resulted in a number ofdifferent proposals, is a method in which a resist pattern is firstformed using photolithography, and subsequent heat treatment is thenused to further reduce the size of the resist pattern.

For example, the patent reference 2 discloses an omission patternformation method in which an omission pattern is first formed in apattern formation resist applied to the surface of a substrate, a mixinggeneration resist that mixes with the pattern formation resist is thenapplied across the entire surface of the substrate, baking is performedso that a mixed layer is formed on the side walls and the surface of thepattern formation resist, and the unmixed sections of the mixinggeneration resist are then removed, enabling the pattern size to bereduced by the dimensions of the mixed layer.

Furthermore, the patent reference 3 discloses a pattern formation methodin which a resist pattern comprising an acid generator is formed on asubstrate, the entire surface of the substrate is coated with a resinthat becomes insoluble in the presence of acid, a heat treatment is thenconducted, causing acid to diffuse from the resist into the resin,forming a resist layer of uniform thickness at the interface between theresin and the resist pattern, and developing is then used to removethose sections of the resin into which the acid has not diffused,thereby enabling the pattern size to be reduced by the dimension of theaforementioned uniform thickness.

Furthermore, recently, thermal flow processes in which the resistpattern is fluidized through heat treatment or the like, therebyenabling a reduction in the pattern size, have also been proposed. In athermal flow method, a resist pattern is first formed usingphotolithography, and by subsequently heating the pattern to atemperature exceeding the glass transition temperature (Tg) of the resincomponent within the resist layer, thereby softening the resist, thesize of the resist pattern is reduced.

For example, the patent reference 4 discloses a method of forming a finepattern in which a resist pattern is formed on a substrate, heattreatment is conducted, and the cross sectional shape of the resistpattern is changed from a rectangular shape to a semicircle, therebyincreasing the length of the base and forming a finer pattern.

Furthermore, the patent reference 5 discloses a method of forming a finepattern in which following formation of a resist pattern, heating isconducted to approximately the softening temperature of the resistpattern, and fluidization of the resist causes a narrowing of thepattern size.

(Patent Reference 1)

Japanese Unexamined Patent Application, First Publication No.2002-162745

(Patent Reference 2)

Japanese Unexamined Patent Application, First Publication No. Hei5-166717

(Patent Reference 3)

Japanese Unexamined Patent Application, First Publication No. Hei5-241348

(Patent Reference 4)

Japanese Unexamined Patent Application, First Publication No. Hei1-307228

(Patent Reference 5)

Japanese Unexamined Patent Application, First Publication No. Hei4-364021

As described above, in those cases where heat treatment is performed onthe resist following resist pattern formation (and followingdeveloping), the pattern size of the resist pattern, namely, the size ofthe sections in which the resist is not formed (such as the holediameter within a hole pattern or the space width within a line andspace (L&S) pattern) reduces relative to the size prior to the heattreatment. In such cases, if a conventional ArF resist is used, thedegree to which the pattern size reduces (the degree of narrowing)differs for differing patterns even on the same substrate, resulting ina problem that resist patterns of different pattern sizes can be formedon a single substrate (namely, variation can develop in the narrowedresist pattern size).

DISCLOSURE OF INVENTION

Accordingly, an object of the present invention is to provide a methodof forming a resist pattern comprising a narrowing step for narrowingthe pattern size of a resist pattern using the above type of heattreatment, wherein the pattern size following the narrowing process iseasily controlled and suffers minimal variation, as well as a positiveresist composition used in such a method, and a layered product usingsuch a positive resist composition.

As a result of intensive research, the inventors of the presentinvention believe that the cause of variations in the pattern size isthe fact that the temperature dependency of the fluidity of conventionalArF resists is very high, so that when heating is conducted at atemperature near the softening point of the resist layer, even veryminor variations in temperature cause the fluidity to alter, therebycausing the degree to which fluidization occurs to vary depending on theposition of the resist pattern, even on a single substrate.

In other words, when heat treatment is conducted on a resist followingdeveloping in order to narrow the pattern size, it is essential that aresist pattern of uniform pattern size is formed on a single substrate,so that the hole diameters of the plurality of holes in a hole patternare uniform, and the space width in a L&S pattern is uniform. In orderto achieve this result, the pattern size preferably reduces by aconstant quantity (namely, the degree of narrowing is constant) relativeto the pattern size following developing (prior to the heat treatment).However, with conventional ArF resists, even very minor variations intemperature cause a variation in the degree of narrowing, meaning thatreducing the pattern size for a plurality of patterns while maintainingthe uniformity that existed prior to the heat treatment is difficult.Consequently, variations in the pattern sizes develop on the samesubstrate, leading to a poorer level of resist pattern uniformity thanthat prior to the heat treatment. This means that, particularly in thecase of semiconductor elements with complex resist patterns, highyielding production can be very difficult.

In addition, the degree of narrowing tends to increase as the exposuredose (exposure time) increases, or as the distance between patterns (thepitch) increases, meaning the uniformity of the obtained resist patterncan deteriorate with variations in the exposure dose or due todifferences in the pitch. Consequently, in the production process,consideration must be given not only to the temperature, but also to theexposure dose and the pitch, resulting in a marked tightening of themargins within the process.

In response to these types of problems, the applicants of the presentinvention have proposed a shrink process as one method of obtaining afine resist pattern with good control of the pattern size (JapaneseUnpublished Patent Application No. 2001-302552, Japanese UnpublishedPatent Application No. 2002-080517), wherein following the formation ofa resist pattern on a substrate, a water soluble resin coating is formedon top of the resist pattern, this water soluble resin coating is shrunkby subsequent heat treatment, and this heat shrinkage action is used tonarrow the size of the resist pattern.

However, even in this type of method, and particularly in the case ofcomplex resist patterns that utilize an ArF resist, satisfactory controlof the pattern size sometimes proves difficult with particularly fineresist patterns.

As a result of intensive investigations aimed at resolving these issues,the inventors of the present invention discovered that by using apositive resist composition comprising, as the base resin, a resin witha structural unit derived from a (meth)acrylate ester of a specificstructure, a resist pattern could be formed with excellent control ofthe pattern size, and were hence able to complete the present invention.

In other words, a first aspect of the present invention for resolvingthe above problems is a method of forming a resist pattern comprising: aresist pattern formation step, in which a positive resist compositioncomprising a resin component (A) that displays increased alkalisolubility under the action of acid, and an acid generator component (B)that generates acid on exposure is applied to a substrate, a prebake isconducted, the resist composition is selectively exposed, post exposurebaking (PEB) is conducted, and alkali developing is then used to form aresist pattern; and a narrowing step in which the pattern size of theproduced resist pattern is narrowed by heat treatment, wherein

the component (A) utilizes a resin with a structural unit (a1) derivedfrom a (meth)acrylate ester represented by a general formula (I) shownbelow:

wherein, R represents a hydrogen atom or a methyl group; X represents ahydrocarbon group with 1 to 4 rings; R¹ to R³ either each represent,independently, a lower alkyl group, or alternatively, one of R¹ to R³represents a lower alkyl group, and the other two groups represent loweralkylene groups, the terminals of which are bonded together to form asingle ring containing 5 or 6 carbon atoms including the bonded terminalcarbon atoms.

A second aspect of the present invention for resolving the aboveproblems is a positive resist composition for use within the abovemethod of forming a resist pattern, comprising a resin component (A)that displays increased alkali solubility under the action of acid, andan acid generator component (B) that generates acid on exposure, whereinthe component (A) is a resin with a structural unit (a1) derived from a(meth)acrylate ester represented by the general formula (I) shown above.

A third aspect of the present invention for resolving the above problemsis a layered product in which a resist layer formed from a positiveresist composition according to the second aspect, and a water solubleresin coating comprising a water soluble polymer on the resist layer arelayered onto a substrate.

In the present invention, the term “lactone unit” refers to a group inwhich one hydrogen atom has been removed from a monocyclic or polycycliclactone. The term “(meth)acrylic acid” refers to acrylic acid and/ormethacrylic acid. The term “(meth)acrylate” refers to acrylate and/ormethacrylate. The term “structural unit” refers to a monomer unit usedin producing a polymer. Furthermore, in the description that follows, a“structural unit derived from a (meth)acrylate ester” may be referred toas a “(meth)acrylate structural unit”.

According to the present invention, a resist pattern with minimalpattern variation within the plane of the substrate, and excellentuniformity can be formed with good control of the pattern size.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are graphs showing the variation in the hole diameter(C.D.) of a hole pattern relative to the exposure (dose), for both thesituation prior to heat treatment, and the situation following heattreatment at a variety of different temperatures according to an example1 (wherein FIG. 1A shows the results for a dense pattern, and FIG. 1Bthe results for an isolated pattern).

FIGS. 2A and 2B are graphs showing the variation in the hole diameter(C.D.) of a hole pattern relative to the exposure (dose), for both thesituation prior to heat treatment, and the situation following heattreatment at a variety of different temperatures according to acomparative example 1 (wherein FIG. 2A shows the results for a densepattern, and FIG. 2B the results for an isolated pattern).

BEST MODE FOR CARRYING OUT THE INVENTION

As follows is a description of embodiments of the present invention,although the present invention is in no way restricted to the examplespresented below.

A characteristic of the present invention is the use of a resincomprising a structural unit (a1) derived from a (meth)acrylate esterrepresented by the general formula (I) shown above as the aforementionedcomponent (A).

The reason why the present invention enables a resist pattern to beformed with good control of the pattern size is not entirely clear,although the following are considered possible reasons. Namely, duringresist pattern formation, light can leak marginally into the unexposedsections at the edges of the exposed sections, and although these edgesections do not become soluble in the developing liquid, a portion ofthe dissolution inhibiting groups within these regions may dissociate.In recent years, halftone phase shift masks have become widely used,particularly in those cases where hole patterns are formed, in order todeal with ever finer resist patterns, and light leakage is more likelyin these types of cases.

At the same time, the base resins of ArF resists use bulky groups suchas adamantyl skeletons containing a tertiary carbon atom as dissolutioninhibiting groups. Consequently, when a dissolution inhibiting groupdissociates, the glass transition temperature (Tg) of the resindecreases considerably. As the Tg of the resin decreases, thetemperature at which the resin undergoes fluidization also decreases.

Accordingly, the resist within those unexposed sections (unexposedsections A) in which a portion of the dissolution inhibiting groups havedissociated, formed as a result of slight light leakage from the edgesections of the exposed sections, are more likely to undergo softeningat a lower temperature than those unexposed sections (unexposed sectionsB) in which none of the dissolution inhibiting groups have dissociated,and even within the unexposed sections A, the temperature at whichsoftening starts varies depending on the proportion of the dissolutioninhibiting groups that have dissociated.

Furthermore, the above types of bulky dissolution inhibiting groupsfunction as plasticizers after dissociating, and this plasticizationeffect increases the flexibility of the resist, making control of thedegree of narrowing even more difficult.

As a result, if a plurality of hole patterns are formed on a singlesubstrate, and heat treatment is then conducted, the resist softens andflows into the hole patterns, reducing the hole diameter of the holepatterns, but the degree to which this inflow occurs varies depending onthe position on the substrate in which the hole pattern is formed.Accordingly, even for hole patterns formed on a single substrate, it isthought that the degree of narrowing varies depending on the position onthe substrate, making control of the pattern size very difficult.

In addition, as described above, this phenomenon is strongly dependenton the level of exposure and the pitch, and it is surmised that thereason for this dependency is as described below. Namely, as theexposure (dose) increases, in other words as the exposure timelengthens, larger numbers of dissolution inhibiting groups dissociatewithin the unexposed sections A described above, meaning the extent bywhich the Tg value is reduced increases, and the range of such Tgreductions widens. As a result, in the case of a hole pattern forexample, the greater the exposure becomes, the more likely it is thatthe resist will soften. Furthermore, it is surmised that the larger thepitch (the distance between patterns) becomes, the greater the volume ofresist will be between adjacent patterns, meaning the quantity of resistflowing into the hole patterns will increase, causing an increaseddegree of narrowing of the hole patterns.

In contrast, it is thought that in the case of a resin of the presentinvention, because the resin must contain the structural unit (a1)described above, and utilizes non-bulky groups as the acid dissociable,dissolution inhibiting groups, the variation in the Tg value ondissociation of a dissolution inhibiting group is minimal, meaning thedegree of narrowing can be maintained at an essentially uniform level.

<<Method of Forming a Resist Pattern>>

A method of forming a resist pattern according to the present inventionutilizes a positive resist composition of the present invention,comprising a resin with a specific structural unit as a resin component(A) that displays increased alkali solubility under the action of acid,and an acid generator component (B) that generates acid on exposure, andcomprises the following steps.

<Resist Pattern Formation Step>

The resist pattern formation step can be conducted using a conventionalresist pattern formation method, such as the method described below.Namely, a positive type resist composition such as that described belowis first applied to the surface of a substrate such as a silicon waferusing a spinner or the like, and a prebake is conducted undertemperature conditions of 80 to 150° C. for 40 to 120 seconds, andpreferably for 60 to 90 seconds, thereby forming a resist film.Following selective exposure of the resist film with an ArF excimerlaser through a desired mask pattern using, for example, an ArF exposureapparatus, PEB (post exposure baking) is conducted under temperatureconditions of 80 to 150° C. for 40 to 120 seconds, and preferably for 60to 90 seconds. Subsequently, developing is conducted using an alkalideveloping liquid such as an aqueous solution of tetramethylammoniumhydroxide with a concentration of 0.05 to 10% by weight, and preferablyfrom 0.05 to 3% by weight. In this manner, a resist pattern which isfaithful to the mask pattern can be obtained.

An organic or inorganic anti-reflective film may also be providedbetween the substrate and the applied layer of the resist composition inorder to improve the resolution. Furthermore, the alkali developingliquid usually employs a standard concentration of 2.38% by weight, butdeveloping is also possible using more dilute developing liquids with aconcentration within a range from 0.05 to 0.5% by weight, and the LERand the pattern shape tend to improve for concentrations within thisrange.

The resist film typically has a film thickness of no more than 1 μm, andis usually formed with a film thickness of 300 to 500 nm, although theincreasing aspect ratios that accompany miniaturization mean thatpattern collapse is becoming a significant problem for ArF excimer laserresists. One method of resolving this issue is to reduce the filmthickness of the resist. However, when a thin film with a film thicknessof 150 to 300 nm is formed, the pattern shape may deteriorate to someextent. In those cases in which this type of thin film is to be formed,a better pattern shape can be produced by marginally increasing thequantity of the component (B), by 2 to 3% for example, relative to thetypically used quantity or the preferred quantity listed below.

[Positive Resist Composition]

The present invention utilizes a positive resist composition, whichcontains, as the aforementioned component (A), a resin that contains atleast a structural unit (a1) derived from a (meth)acrylate esterrepresented by the general formula (I) shown above.

Component (A)

[Structural Unit (a1)]

The structural unit (a1) can be represented by a general formula (II)shown below.

(wherein, R⁴ is a group comprising groups R¹ to R³ and a carbon atombonded thereto (namely, —C(—R¹)(—R²)—R³), and R, X, and R¹ to R³ are asdescribed below.)

The structural unit (a1) is a unit derived from a (meth)acrylate ester,in which the carboxyl group of the (meth)acrylic acid is bonded to thegroup X through an ester linkage, and the group R⁴ is bonded, via anester linkage, to a carboxyl group bonded to a ring within the group X.

In the structural unit (a1), the group R⁴ is an acid dissociable,dissolution inhibiting group, which displays an alkali dissolutioninhibiting effect that causes the entire component (A) to be alkaliinsoluble prior to exposure, but dissociates under the action of acidgenerated from the acid generator following exposure, causing the entirecomponent (A) to become alkali soluble.

In the aforementioned general formula (II), R represents a hydrogen atomor a methyl group, so that when R is a hydrogen atom, an acrylatestructural unit is formed, whereas when R is a methyl group, amethacrylate group is formed.

The groups R¹ to R³ are lower alkyl groups, and preferably straightchain or branched alkyl groups of 1 to 5 carbon atoms, and even morepreferably 1 to 3 carbon atoms. Specific examples include methyl groups,ethyl groups, propyl groups, isopropyl groups, n-butyl groups, isobutylgroups, tert-butyl groups, pentyl groups, isopentyl groups and neopentylgroups. Alternatively, one of the groups R¹ to R³ may be a lower alkylgroup such as those described above, and the other two groups may eachrepresent lower alkylene groups (preferably each containing from 1 to 5carbon atoms, and even more preferably from 2 to 3 carbon atoms), theterminals of which are bonded together to form a single ring containing5 or 6 carbon atoms including the bonded terminal carbon atoms.

For the groups R¹ to R³, lower alkyl groups are particularly preferred,and of these, methyl groups and ethyl groups are the most preferred. Insuch cases, the group R⁴ is a tertiary alkyl group such as a tert-butylgroup or a tert-amyl group, and these groups dissociate in the presenceof acid, and are subsequently gasified during the post exposure baking(PEB) due to their low molecular weight, and consequently do not remainin the resist. Accordingly, the type of plasticization effect describedabove, caused by acid dissociable, dissolution inhibiting groups, is farless likely to arise, and the degree of narrowing can be bettercontrolled.

The group X represents a hydrocarbon group that typically contains from1 to 4, and preferably from 2 to 4 rings, and suitable examples includegroups in which 2 hydrogen atoms have been removed from apolycycloalkane such as a bicycloalkane, a tricycloalkane or atetracycloalkane or the like.

Specific examples include groups in which 2 hydrogen atoms have beenremoved from a polycycloalkane such as adamantane, norbornane,isobornane, tricyclodecane or tetracyclododecane.

Of these, groups in which 2 hydrogen atoms have been removed fromadamantane, groups in which 2 hydrogen atoms have been removed fromnorbornane, and groups in which 2 hydrogen atoms have been removed fromtetracyclododecane are preferred from an industrial viewpoint.

Furthermore, the carboxyl group residues of the —CO₂R⁴ group and the(meth)acrylate structural unit may be bonded to any position on therings of the group X, as shown in the following formulas.

For example, in the case in which X is a group in which 2 hydrogen atomshave been removed from tetracyclododecane, the —CO₂R⁴ group may bebonded to position 3 or 4 within the tetracyclododecane skeletonrepresented by the general formula shown below.

However, these bonding positions result in a mixture of stereoisomers,and so the bonding position cannot be specified. Similarly, the carboxylgroup residue of the (meth)acrylate structural unit may be bonded toeither position 8 or 9, although the position cannot be specified.

Furthermore, in the case in which X is a group in which 2 hydrogen atomshave been removed from adamantane, the —CO₂R⁴ group may be bonded toposition 1 or 2 within the adamantane skeleton represented by thegeneral formula shown below.

Similarly, the carboxyl group residue of the (meth)acrylate structuralunit may be bonded to either position 6 or 7.

The structural unit (a1) typically accounts for 30 to 70 mol %, andpreferably from 40 to 60 mol % of the total of all the structural unitswithin the component (A). By ensuring this quantity exceeds the lowerlimit of the above range, the solubility of the polymer becomes morereadily altered in the presence of acid, in those cases where thecomponent (A) is used within a positive resist composition. If thequantity exceeds the upper limit of the above range, there is a dangerof problems that the functions of the other structural units are notsufficiently displayed.

The component (A) may also contain any of the optional structural units(a2) to (a5) described below.

(a2): a (meth)acrylate structural unit containing a lactone unit

(a3): a structural unit derived from a (meth)acrylate containing ahydroxyl group

(a4): a (meth)acrylate structural unit with an acid dissociable,dissolution inhibiting group that is different from the structural unit(a1)

(a5): other structural units different from any of the structural units(a1) to (a4)

[Structural Unit (a2)]

A lactone unit, namely a group in which one hydrogen atom has beenremoved from a monocyclic or polycyclic lactone, is a polar group, andconsequently when the component (A) is used as a positive resistcomposition, the structural unit (a2) is effective in increasing theadhesion between the resist film and the substrate, and improving theaffinity with the developing liquid.

There are no particular restrictions on the structural unit (a2),provided it contains this type of lactone unit.

Examples of the lactone unit include groups in which one hydrogen atomhas been removed from the lactones shown in the structural formulasbelow.

Furthermore in the structural unit (a2), the lactone unit is preferablyat least one unit selected from a group consisting of compounds of thegeneral formula (III) and the general formula (IV) shown below.

Specific examples of the structural unit (a2) include the (meth)acrylatestructural units represented by the structural formulas shown below.

(wherein, R is a hydrogen atom or a methyl group)

(wherein, R is a hydrogen atom or a methyl group)

(wherein, R is a hydrogen atom or a methyl group)

(wherein, R is a hydrogen atom or a methyl group, and m is either 0 or1)

Of the above structural units, γ-butyrolactone esters of (meth)acrylicacid with an ester linkage at the α carbon atom (formula 11), ornorbornane lactone esters (formula 9), are particularly preferred interms of industrial availability.

The structural unit (a2) typically accounts for 20 to 60 mol %, andpreferably from 30 to 50 mol % of the total of all the structural unitswithin the component (A). By ensuring the quantity exceeds the lowerlimit of the above range, the adhesion can be improved, whereas if thequantity exceeds the upper limit of the above range, there is a dangerof a deterioration in resolution.

[Structural Unit (a3)]

Because the structural unit (a3) contains a hydroxyl group, use of thestructural unit (a3) results in an increased affinity with thedeveloping liquid for the entire component (A), and an improvement inthe alkali solubility of the exposed sections of the resist.Accordingly, the structural unit (a3) contributes to an improvement inthe resolution.

The structural unit (a3) can be appropriately selected from themultitude of ArF excimer laser resist composition resins that have beenproposed, and polycyclic groups containing hydroxyl groups arepreferred.

Suitable examples of the polycyclic group include the various groupslisted as suitable examples of the group X in the above description forthe structural unit (a1).

Specifically, preferred examples of the structural unit (a3) includehydroxyl group containing adamantyl groups (in which the number ofhydroxyl groups is preferably from 1 to 3, and most preferably 1), andcarboxyl group containing tetracyclododecanyl groups (in which thenumber of carboxyl groups is from 1 to 2, and most preferably 1).Carboxyl group containing tetracyclododecanyl groups are particularlypreferred.

Specifically, if the structural unit (a3) has a structure represented bya general formula (V) shown below, then the dry etching resistanceimproves, as does the verticalness of the pattern cross-section, both ofwhich are desirable.

(wherein, R represents a hydrogen atom or a methyl group)

The structural unit (a3) typically accounts for 0 to 30 mol %, andpreferably from 5 to 15 mol % of the total of all the structural unitswithin the component (A). By ensuring the quantity exceeds the lowerlimit of the above range, the resolution can be improved, whereas if thequantity exceeds the upper limit of the above range, there is a dangerthat the functions of the other structural units are not sufficientlydisplayed.

[Structural Unit (a4)]

In the present invention, the component (A) may also contain a(meth)acrylate structural unit with an acid dissociable, dissolutioninhibiting group that is different from the structural unit (a1),provided such addition does not impair the effects of the presentinvention. From the viewpoint of achieving maximum effect from thepresent invention, structural units containing acid dissociable,dissolution inhibiting groups are most preferably restricted to only thestructural unit (a1).

The structural unit (a4) can be appropriately selected from themultitude of units in ArF excimer laser resist composition resins thathave been proposed, although adding a structural unit containing apolycyclic acid dissociable, dissolution inhibiting group is preferredfrom the viewpoints of improving compression dependency and patternshape.

Specifically, the structural unit (a4) is preferably at least one unitselected from a group consisting of the general formulas (VI) and (VII)shown below.

(wherein, R represents a hydrogen atom or a methyl group, and R¹¹represents a lower alkyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R¹² andR¹³ each represent, independently, a lower alkyl group)

The structural unit represented by the general formula (VI) is a(meth)acrylate structural unit with a hydrocarbon group bonded throughan ester linkage, and by bonding a straight chain or a branched alkylgroup to the carbon atom of the adamantyl group that is adjacent to theoxygen atom (—O—) of the ester function, a tertiary alkyl group isformed within the ring skeleton of the adamantyl group.

Within the above formula, the group R¹¹ is preferably a straight chainor branched alkyl group of 1 to 5 carbon atoms, and specific examplesinclude a methyl group, ethyl group, propyl group, isopropyl group,n-butyl group, isobutyl group, tert-butyl group, pentyl group, isopentylgroup and neopentyl group. Of these, an alkyl group of at least 2 carbonatoms, and preferably 2 to 5 carbon atoms is preferred, and in suchcases, the acid dissociability tends to increase compared with the casein which R¹¹ is a methyl group. In terms of industrial availability, amethyl group is the most desirable.

The (meth)acrylate structural unit represented by the aforementionedgeneral formula (VII), like the general formula (VI), is a(meth)acrylate structural unit with a bonded hydrocarbon group, althoughin this case, the carbon atom adjacent to the oxygen atom (—O—) of theester function of the (meth)acrylate structural unit is a tertiary alkylgroup, and a ring skeleton such as an adamantyl group exists within thistertiary alkyl group.

The groups R¹² and R¹³ each preferably represent, independently, a loweralkyl group of 1 to 5 carbon atoms. These types of groups tend todisplay a higher acid dissociability than a 2-methyl-2-adamantyl group.

Specifically, the groups R¹² and R¹³ each represent, independently, thesame types of straight chain or branched lower alkyl groups describedabove for R¹¹. Of these groups, the case in which R¹² and R¹³ are bothmethyl groups is preferred from an industrial viewpoint.

The structural unit (a4) typically accounts for no more than 30 mol %,and preferably no more than 20 mol % of the total of all the structuralunits within the component (A). By including the structural unit (a4),the polymer solubility can be more readily altered through the action ofacid, in those cases where the component (A) is used in a positiveresist composition, but if the quantity of the structural unit (a4)exceeds the upper limit of the above range, there is a danger of adeterioration in the effects of the present invention.

[Structural Unit (a5)]

There are no particular restrictions on the structural unit (a5), whichcan be any other structural unit that cannot be classified as one of thestructural units (a1) to (a4). In other words, any structural unit thatdoes not contain an acid dissociable, dissolution inhibiting group, alactone or a hydroxyl group can be included as the structural unit (a5).Structural units that contain a polycyclic group and are derived from a(meth)acrylate ester are preferred. If this type of structural unit isused, then when the component (A) is used for a resist composition, theresolution for isolated patterns through to semi dense patterns (lineand space patterns in which for a line width of 1, the space width iswithin a range from 1.2 to 2) is excellent, and consequently preferred.

Examples of the polycyclic group include the various groups listed assuitable examples of the group X in the above description for thestructural unit (a1), and any of the multitude of materialsconventionally used within ArF positive resist materials or KrF positiveresist materials can be used.

From the viewpoint of industrial availability, at least one of atricyclodecanyl group, an adamantyl group or a tetracyclododecanyl groupare preferred.

Specific examples of the structural unit (a5) include the structuresrepresented by the general formulas (VIII) to (X) shown below.

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

Compositions in which the structural unit (a5) accounts for 1 to 25 mol%, and preferably from 10 to 20 mol % of the total of all the structuralunits within the component (A) display excellent resolution for isolatedpatterns through to semi dense patterns, and are consequently preferred.

Amongst the different structural units of the component (A), thestructural units (a2) to (a5) can be appropriately selected and combinedwith the structural unit (a1) in accordance with the target application.Depending on the application, other structural units may also be used inaddition to the structural units from (a1) to (a5).

For example, in the case of a polymer formed from a combination ofstructural units with acid dissociable, dissolution inhibiting groups,namely the structural unit (a1) and an optional structural unit (a4),together with the structural unit (a2), the structural units with aciddissociable, dissolution inhibiting groups typically account for 20 to70 mol %, and preferably from 40 to 60 mol % of the total of all thestructural units, and the structural unit (a2) accounts for 30 to 80 mol%, and preferably from 40 to 60 mol %.

Furthermore, in the case of a polymer which in addition to the abovecomponents also contains the structural unit (a3), the structural unitswith acid dissociable, dissolution inhibiting groups typically accountfor 20 to 70 mol %, and preferably from 40 to 60 mol % of the total ofall the structural units, the structural unit (a2) accounts for 20 to 60mol %, and preferably from 30 to 50 mol %, and the structural unit (a3)account for 1 to 20 mol %, and preferably from 5 to 15 mol % of thetotal of all the structural units.

The component (A) comprises a structural unit (a1^(a)) derived from anacrylate ester and/or a structural unit (a1^(m)) derived from amethacrylate ester as the structural unit (a1).

Similarly, the other structural units (a2), (a3), (a4) and (a5) alsocomprise structural units derived from acrylic acid and/or methacrylicacid.

There are no particular restrictions on the weight average molecularweight (Mw) (polystyrene equivalent) of the component (A), althoughvalues within a range from 4,000 to 30,000 are preferred, and valuesfrom 7,000 to 15,000 are even more desirable. If the molecular weight isgreater than this range, then there is a danger of a deterioration inthe solubility of the component in the resist solvent, whereas if themolecular weight is too small, there is a danger of a deterioration inthe cross sectional shape of the resist pattern.

Furthermore, there are no particular restrictions on the value ofMw/(number average molecular weight (Mn)), although values within arange from 1.0 to 6.0 are preferred, and values from 1.5 to 2.5 are evenmore desirable. If the value is greater than this range, the resolutionand the pattern shape tend to deteriorate.

The polymer of the component (A) can be produced easily by aconventional radical polymerization of the corresponding (meth)acrylateester monomers, using a radical polymerization initiator such asazobisisobutyronitrile (AIBN).

Component (B)

The component (B) can be appropriately selected from known materialsused as acid generators in conventional chemically amplified resists.

Specific examples of the component (B) include onium salts such asdiphenyliodonium trifluoromethanesulfonate,(4-methoxyphenyl)phenyliodonium trifluoromethanesulfonate,bis(p-tert-butylphenyl)iodonium trifluoromethanesulfonate,triphenylsulfonium trifluoromethanesulfonate,(4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,(4-methylphenyl)diphenylsulfonium nonafluorobutanesulfonate,(p-tert-butylphenyl)diphenylsulfonium trifluoromethanesulfonate,diphenyliodonium nonafluorobutanesulfonate,bis(p-tert-butylphenyl)iodonium nonafluorobutanesulfonate andtriphenylsulfonium nonafluorobutanesulfonate. Of these, onium salts witha fluorinated alkylsulfonate ion as the anion are preferred.

This component (B) may utilize a single compound, or a combination oftwo or more compounds. The quantity added is preferably selected withina range from 0.5 to 30 parts by weight, and even more preferably from 1to 10 parts by weight per 100 parts by weight of the component (A). Ifthe quantity is less than 0.5 parts by weight then there is a danger ofthe pattern formation not proceeding satisfactorily, whereas if thequantity exceeds 30 parts by weight, then achieving a uniform solutionbecomes difficult, and there is a danger of a deterioration in storagestability.

A resist composition of the present invention is produced by dissolvingthe component (A) and the component (B), together with an optionalcomponent described below, preferably in an organic solvent.

The organic solvent can be any solvent capable of dissolving thecomponent (A) and the component (B) to generate a uniform solution, andthe solvent used can be one, or two or more solvents selected fromamongst known solvents used for conventional chemically amplifiedresists.

Specific examples of the solvent include ketones such as acetone, methylethyl ketone, cyclohexanone, methyl isoamyl ketone and 2-heptanone;polyhydric alcohols and derivatives thereof such as ethylene glycol,ethylene glycol monoacetate, diethylene glycol, diethylene glycolmonoacetate, propylene glycol, propylene glycol monoacetate, dipropyleneglycol, or the monomethyl ether, monoethyl ether, monopropyl ether,monobutyl ether or monophenyl ether of dipropylene glycol monoacetate;cyclic ethers such as dioxane; and esters such as methyl lactate, ethyllactate, methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate,ethyl pyruvate, methyl methoxypropionate, and ethyl ethoxypropionate.These organic solvents can be used singularly, or as a mixed solvent oftwo or more different solvents.

In particular, mixed solvents of propylene glycol monomethyl etheracetate (PGMEA) and a polar solvent containing a hydroxyl group or alactone such as propylene glycol monomethyl ether (PGME), ethyl lactate(EL) or γ-butyrolactone offer good improvement in the storage stabilityof the positive resist composition, and are consequently preferred.

In those cases where EL is added, the weight ratio of PGMEA:EL ispreferably within a range from 6:4 to 4:6.

In those cases in which PGME is added, the weight ratio of PGMEA:PGME istypically within a range from 8:2 to 2:8, and preferably from 8:2 to5:5.

Mixed solvents of PGMEA and PGME improve the storage stability of thepositive resist composition in those cases in which the component (A)comprises all of the structural unit (a1) and optionally structural unit(a4), the structural unit (a2), the structural unit (a3) and thestructural unit (a5), and are consequently preferred.

Mixed solvents containing at least one of PGMEA and ethyl lactate,together with γ-butyrolactone are also preferred as the organic solvent.In such cases, the weight ratio of the former and latter components inthe mixed solvent is preferably within a range from 70:30 to 95:5. Thereare no particular restrictions on the quantity of the organic solvent,although typically, a sufficient quantity of the solvent is added toproduce a combined solid fraction concentration of 5 to 50% by weight,and preferably from 7 to 20% by weight, in accordance with the resistapplication film pressure.

In a positive resist composition of the present invention, in order toimprove the resist pattern shape and the long term stability (the postexposure stability of the latent image formed by the pattern wiseexposure of the resist layer), a secondary lower aliphatic amine or atertiary lower aliphatic amine can also be added as a separate, optionalcomponent.

Here, a lower aliphatic amine refers to an alkyl or alkyl alcohol amineof no more than 5 carbon atoms, and examples of these secondary andtertiary amines include trimethylamine, diethylamine, triethylamine,di-n-propylamine, tri-n-propylamine, tripentylamine, diethanolamine andtriethanolamine, and alkanolamines such as triethanolamine arepreferred.

These may be used singularly, or in combinations of two or moredifferent compounds.

These types of amines are typically added in quantities within a rangefrom 0.01 to 1.0% by weight relative to the quantity of the component(A).

Miscible additives can also be added to a positive resist composition ofthe present invention according to need, including additive resins forimproving the properties of the resist film, surfactants for improvingthe ease of application, dissolution inhibitors, plasticizers,stabilizers, colorants and halation prevention agents.

In terms of the light source used in the exposure process, although apositive resist composition of the present invention is particularlyapplicable to ArF excimer lasers, it is also effective for other typesof radiation, including radiation of longer wavelength such as KrFexcimer lasers, and radiation of shorter wavelength such as F₂ excimerlasers, EUV (extreme ultraviolet radiation), VUV (vacuum ultravioletradiation), electron beams, X-rays and soft X-rays.

<Narrowing Step>

In the present invention, the narrowing step is performed followingdevelopment of the resist pattern, in order to narrow the pattern sizeof the resist pattern.

Thermal Flow Process

One method that can be favorably used for the narrowing step is a methodknown as a thermal flow process.

A thermal flow process can be carried out in the manner described below.Namely, the developed resist pattern is heated at least once, andpreferably 2 to 3 times, to soften the resist, and by causing the resistto flow, the pattern size of the resist pattern (such as the holediameter within a hole pattern or the space width within a line andspace pattern) is shrunk to a smaller value than that immediatelyfollowing developing.

The ideal heating temperature depends on the actual composition of thepositive resist composition, although there are no particularrestrictions on the temperature provided it exceeds the softening pointof the resist pattern. Temperatures within a range from 80 to 180° C.are preferred, and temperatures from 110 to 150° C. are even moredesirable. Keeping the heating temperature within the above range offerscertain advantages, including easier control of the pattern size.

Furthermore, there are no particular restrictions on the ideal heatingtime, and any time period that enables production of the desired patternsize without impairing throughput is suitable. In terms of applicationto a typical semiconductor element production line, a single heatingprocess of 10 to 300 seconds, and preferably from 30 to 180 seconds isdesirable.

Furthermore, in the case of a thermal flow process, the positive resistcomposition is preferably a composition containing a compound with atlest two vinyl ether groups (hereafter referred to as the component(C)), which on heating undergoes a cross linking reaction with thecomponent (A). This type of positive resist composition offers evenbetter control of the pattern size. It is thought that the reason forthis enhanced control is that because the heating causes cross linking,which increases the Tg value of the formed resist, any reduction in theTg value when the resist pattern undergoes softening during the heatingof the narrowing step can be suppressed.

There are no particular restrictions on the component (C), provided thatwhen the resist composition is applied to the substrate and dried toform the resist film, the component (C) undergoes cross linking with thecomponent (A) during the heating process. Preferred examples of thecomponent (C) include compounds in which at least 2 hydroxyl groups ofeither a polyoxyalkylene glycol such as an alkylene glycol, dialkyleneglycol or trialkylene glycol, or a polyhydric alcohol such astrimethylolpropane, pentaerythritol or pentaglycol have been substitutedwith vinyl ethers.

Specific examples of such compounds include ethylene glycol divinylether, diethylene glycol divinyl ether, triethylene glycol divinylether, 1,4-butanediol divinyl ether, tetramethylene glycol divinylether, tetraethylene glycol divinyl ether, neopentyl glycol divinylether, trimethylolpropane trivinyl ether, trimethylolethane trivinylether, hexanediol divinyl ether, 1,4-cyclohexanediol divinyl ether,tetraethylene glycol divinyl ether, pentaerythritol divinyl ether,pentaerythritol trivinyl ether, and cyclohexanedimethanol divinyl ether.Of these, divinyl ethers of alkylene glycols with an alicyclic groupsuch as cyclohexanedimethanol divinyl ether are particularly preferred.

This cross linking compound with at least two vinyl ether groups of thecomponent (C) is typically added at a rate of 0.1 to 25 parts by weight,and preferably from 1 to 15 parts by weight, per 100 parts by weight ofthe component (A). The component (C) may utilize either a singlecompound, or a mixture of two or more different compounds.

Shrink Process

Another example of an ideal process for the narrowing step is the shrinkprocess that has been proposed by the applicants of the presentinvention.

In this shrink process, a resist pattern formed on a substrate is coatedwith a water soluble resin coating, and this water soluble resin coatingis shrunk by subsequent heat treatment, and this heat shrinkage actionis used to narrow the spacing in the resist pattern.

More specifically, first a coating formation agent comprising a watersoluble polymer is applied to the surface of a resist pattern formed ona substrate, preferably forming a layered product in which the watersoluble resin coating covers the entire surface of the resist pattern.Following application of the coating formation agent, a prebake may beconducted at a temperature of 80 to 100° C. for a period of 30 to 90seconds. The application of the coating agent can be conducted using aknown method used in the formation of conventional resist layers and thelike. In other words, the aqueous solution of the coating formationagent can be applied to the substrate using a spinner or the like.

Subsequently, the thus obtained layered product is subjected to heattreatment, causing the water soluble resin coating to undergo heatshrinkage. As a result of this heat shrinkage of the water soluble resincoating, the side walls of the resist patterns adjacent to the watersoluble resin coating are pulled together, thereby narrowing the spacingbetween patterns. This photoresist pattern spacing determines the finalpattern size (the hole diameter within a hole pattern or the widthwithin a line and space pattern), and consequently the heat shrinkage ofthe water soluble resin coating is able to narrow the pattern size,enabling a further miniaturization of the pattern.

The heating temperature is set to the temperature required to achieveshrinkage of the water soluble resin coating, and there are noparticular restrictions on this temperature provided satisfactorynarrowing of the pattern size can be achieved, although the heating ispreferably conducted at a temperature that is less than the softeningpoint of the resist pattern. Conducting the heat treatment at this typeof temperature is extremely beneficial, as it enables a pattern with agood profile to be formed more effectively, and also reduces the pitchdependency of the degree of narrowing within the substrate plane, thatis, the degree to which the level of narrowing is dependent on thepattern size within the substrate plane.

The “softening point” of the resist pattern refers to the temperature atwhich the photoresist pattern formed on the substrate begins to flowspontaneously during heat treatment of the substrate. The softeningpoint of the resist pattern varies depending on the resist compositionused to form the resist pattern. Taking into consideration the softeningpoints of the various resist compositions used in current lithographytechniques, a preferred heat treatment is typically conducted at atemperature within a range from 80 to 160° C., at a temperature thatdoes not cause fluidization of the resist, for a period of 30 to 90seconds.

The thickness of the water soluble resin coating is preferably eitherapproximately equal to the height of the photoresist pattern, or of aheight sufficient to cover the resist pattern, and is typically within arange from 0.1 to 0.5 μm.

Subsequently, the heat shrunk water soluble resin coating, which stillremains on the pattern, is removed by washing with an aqueous solvent,and preferably with pure water, for 10 to 60 seconds. The water solubleresin coating is easily removed by washing with water, and is able to becompletely removed from the substrate and the resist pattern.

There are no particular restrictions on the water soluble polymercontained within the coating formation agent used to form the watersoluble resin coating, provided the polymer is soluble in water at roomtemperature, although resins comprising structural units derived from atleast one monomer which acts as a proton donor, and structural unitsderived from at least one monomer which acts as a proton acceptor areideal. By using this type of resin, volumetric shrinkage can befavorably carried out by heating.

This type of water soluble polymer may also be a copolymer comprisingstructural units derived from at least one monomer which acts as aproton donor, and structural units derived from at least one monomerwhich acts as a proton acceptor, or a mixture of a polymer withstructural units derived from at least one monomer which acts as aproton donor, and a polymer with structural units derived from at leastone monomer which acts as a proton acceptor, although when co-solubilityis taken into consideration, a copolymer is preferred.

From an industrial viewpoint, this water soluble polymer is preferablyan acrylic based polymer, a vinyl based polymer, a cellulose derivative,an alkylene glycol based polymer, a urea based polymer, a melamine basedpolymer, an epoxy based polymer or an amide based polymer.

Specific examples of suitable acrylic based polymers include polymers orcopolymers formed from component monomers such as acrylic acid,acrylamide, methyl acrylate, methacrylic acid, methyl methacrylate,N,N-dimethylacrylamide, N,N-dimethylaminopropylmethacrylamide,N,N-dimethylaminopropylacrylamide, N-methylacrylamide, diacetoneacrylamide, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethylmethacrylate, N,N-dimethylaminoethyl acrylate, and acryloyl morpholine.

Specific examples of suitable vinyl based polymers include polymers orcopolymers formed from component monomers such as morpholine,N-vinylpyrrolidone, vinylimidazolidinone, and vinyl acetate.

Specific examples of suitable cellulose derivatives includehydroxypropyl methylcellulose phthalate, hydroxypropyl methylcelluloseacetate phthalate, hydroxypropyl methylcellulose hexahydrophthalate,hydroxypropyl methylcellulose acetate succinate, hydroxypropylmethylcellulose, hydroxypropyl cellulose, hydroxyethyl cellulose,cellulose acetate hexahydrophthalate, carboxymethylcellulose,ethylcellulose, and methylcellulose.

Specific examples of suitable alkylene glycol based polymers includeaddition polymers or addition copolymers of ethylene glycol or propyleneglycol or the like.

Specific examples of suitable urea polymers include polymers formed frommonomer components such as methylolated urea, dimethylolated urea, andethylene urea.

Specific examples of suitable melamine polymers include polymers formedfrom monomer components such as methoxymethylated melamine,methoxymethylated isobutoxymethylated melamine, and methoxyethylatedmelamine.

In addition, water soluble epoxy based polymers and nylon based polymerscan also be used.

Of the above polymers, a composition comprising at least one polymerselected from a group consisting of alkylene glycol based polymers,cellulose based polymers, vinyl based polymers and acrylic basedpolymers is preferred, and acrylic resins are the most preferred as theyalso offer simple pH adjustment. In addition, using a copolymer of anacrylic based monomer, and another non-acrylic monomer capable offorming a water soluble polymer is preferred, as such copolymers enableefficient narrowing of the photoresist pattern size, while maintainingthe shape of the photoresist pattern during the heat treatment. Thewater soluble polymer may be either a single polymer, or a mixture oftwo or more polymers.

The monomer which acts as a proton donor is preferably acrylamide orN-vinylpyrrolidone.

The monomer which acts as a proton acceptor is preferably acrylic acidor the like.

A water soluble polymer comprising polymer structural units derived fromN-vinylpyrrolidone as the proton donor monomer, and polymer structuralunits derived from acrylic acid as the proton acceptor monomer isparticularly preferred.

In those cases in which the water soluble polymer utilizes a copolymer,there are no particular restrictions on the relative proportions of thestructural components, although if long term stability is consideredparticularly important, then the proportion of the acrylic based polymeris preferably greater than that of other structural polymers. In orderto improve the long term stability, in addition to increasing theproportion of the acrylic based polymer as described above, an acidiccompound such as p-toluenesulfonic acid or dodecylbenzenesulfonic acidcan also be added.

The coating formation agent preferably also contains a surfactant. Thereare no particular restrictions on the surfactant, although thesurfactant should have properties such that when added to the watersoluble polymer described above, the solubility is good, a suspensiondoes not develop, and co-solubility with the polymer component isfavorable. By using a surfactant that satisfies these types ofcharacteristics, the conventional problem of defects, which are thoughtto be related to the occurrence of microfoam during the application ofthe coating material, can be more effectively prevented.

Specifically, one or more surfactants selected from a group consistingof N-alkylpyrrolidone based surfactants, quaternary ammonium salt basedsurfactants, and polyoxyethylene phosphate ester based surfactants ispreferred.

Amongst N-alkylpyrrolidone based surfactants, compounds represented by ageneral formula (XI) shown below are preferred.

(wherein, R²¹ represents an alkyl group of 6 or more carbon atoms)

Specific examples of such N-alkylpyrrolidone based surfactants includeN-hexyl-2-pyrrolidone, N-heptyl-2-pyrrolidone, N-octyl-2-pyrrolidone,N-nonyl-2-pyrrolidone, N-decyl-2-pyrrolidone, N-undecyl-2-pyrrolidone,N-dodecyl-2-pyrrolidone, N-tridecyl-2-pyrrolidone,N-tetradecyl-2-pyrrolidone, N-pentadecyl-2-pyrrolidone,N-hexadecyl-2-pyrrolidone, N-heptadecyl-2-pyrrolidone, andN-octadecyl-2-pyrrolidone. Of these, N-octyl-2-pyrrolidone (“SurfadoneLP100”, manufactured by ISP Co., Ltd.) is preferred.

Amongst quaternary ammonium salt based surfactants, compoundsrepresented by a general formula (XII) shown below are preferred.

(wherein, R²², R²³, R²⁴ and R²⁵ each represent, independently, an alkylgroup or a hydroxyalkyl group (although at least one of the groupsrepresents an alkyl group or a hydroxyalkyl group of 6 or more carbonatoms); and X⁻ represents a hydroxide ion or a halogen ion)

Specific examples of such quaternary ammonium salt based surfactantsinclude dodecyltrimethylammonium hydroxide, tridecyltrimethylammoniumhydroxide, tetradecyltrimethylammonium hydroxide,pentadecyltrimethylammonium hydroxide, hexadecyltrimethylammoniumhydroxide, heptadecyltrimethylammonium hydroxide, andoctadecyltrimethylammonium hydroxide. Of these,hexadecyltrimethylammonium hydroxide is preferred.

Amongst polyoxyethylene phosphate ester based surfactants, compoundsrepresented by a general formula (XIII) shown below are preferred.

(wherein, R²⁶ represents an alkyl group or alkylallyl group of 1 to 10carbon atoms; R²⁷ represents a hydrogen atom or a (CH₂CH₂O)R²⁶ group(wherein R²⁶ as is defined above); and n represents an integer from 1 to20)

Specific examples of such polyoxyethylene phosphate ester basedsurfactants include “Plysurf A212E” and “Plysurf A210G”, which arecommercial products manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.

The quantity added of the surfactant is preferably within a range from0.1 to 10% by weight, and even more preferably from 0.2 to 2% by weight,relative to the total solid fraction of the coating formation agent.Quantities outside the above range can cause a deterioration in the easeof application, resulting in variations in the degree of patternshrinkage as a result of a decrease in in-plane uniformity, and anincreased likelihood of defects, which are thought to be related to theoccurrence of fine bubbles known as microfoam that can be generatedduring application of the coating material.

From the viewpoints of preventing impurities and enabling pH adjustment,the coating formation agent may also contain an optional water solubleamine.

Examples of this water soluble amine include those amines with a pKavalue (acid dissociation constant) in an aqueous solution at 25° C. of7.5 to 13. Specific examples of suitable amines include alkanolaminessuch as monoethanolamine, diethanolamine, triethanolamine,2-(2-aminoethoxy)ethanol, N,N-dimethylethanolamine,N,N-diethylethanolamine, N,N-dibutylethanolamine, N-methylethanolamine,N-ethylethanolamine, N-butylethanolamine, N-methyldiethanolamine,monoisopropanolamine, diisopropanolamine, and triisopropanolamine;polyalkylene polyamines such as diethylenetriamine,triethylenetetramine, propylenediamine, N,N-diethylethylenediamine,1,4-butanediamine, N-ethyl-ethylenediamine, 1,2-propanediamine,1,3-propanediamine, and 1,6-hexanediamine; aliphatic amines such as2-ethyl-hexylamine, dioctylamine, tributylamine, tripropylamine,triallylamine, heptylamine, and cyclohexylamine; aromatic amines such asbenzylamine and diphenylamine; and cyclic amines such as piperazine,N-methyl-piperazine, methyl-piperazine, and hydroxyethylpiperazine. Ofthese, amines with boiling points of 140° C. (760 mmHg) or higher arepreferred, and monoethanolamine and triethanolamine are particularlypreferred.

In those cases in which a water soluble amine is added, the quantity ofthe amine is preferably within a range from 0.1 to 30% by weight, andeven more preferably from 2 to 15% by weight, relative to the totalsolid fraction of the coating formation agent. If the quantity is lessthan 0.1% by weight then there is a danger of a deterioration of thesolution over time, whereas in contrast, if the quantity exceeds 30% byweight, there is a danger of a deterioration in the shape of thephotoresist pattern.

From the viewpoints of reducing the photoresist pattern size andsuppressing the occurrence of defects, an additional non-amine basedwater soluble organic solvent may also be added if desired.

This non-amine based water soluble organic solvent may be any non-aminebased organic solvent that displays miscibility with water, and suitableexamples include sulfoxides such as dimethylsulfoxide; sulfones such asdimethyl sulfone, diethyl sulfone, bis(2-hydroxyethyl) sulfone, andtetramethylene sulfone; amides such as N,N-dimethyl form amide,N-methylformamide, N,N-dimethylacetamide, N-methylacetamide, andN,N-diethylacetamide; lactams such as N-methyl-2-pyrrolidone,N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone,N-hydroxymethyl-2-pyrrolidone, and N-hydroxyethyl-2-pyrrolidone;imidazolidinones such as 1,3-dimethyl-2-imidazolidinone,1,3-diethyl-2-imidazolidinone, and 1,3-diisopropyl-2-imidazolidinone;and polyhydric alcohols or derivatives thereof such as ethylene glycol,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,ethylene glycol monobutyl ether, ethylene glycol monomethyl etheracetate, ethylene glycol monoethyl ether acetate, diethylene glycol,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobutyl ether, propylene glycol, propylene glycolmonomethyl ether, glycerol, 1,2-butylene glycol, 1,3-butylene glycol,and 2,3-butylene glycol. Of these, from the viewpoints of reducing thephotoresist pattern size and suppressing the occurrence of defects,polyhydric alcohols or their derivatives are preferred, and glycerol isparticularly preferred. This non-amine based water soluble organicsolvent can utilize either a single compound, or a mixture of two ormore compounds.

In those cases in which a non-amine based water soluble organic solventis added, the quantity of the solvent is preferably within a range from0.1 to 30% by weight, and even more preferably from 0.5 to 15% byweight, relative to the water soluble polymer. If the quantity is lessthan 0.1% by weight then the defect suppression effect tends to weaken,whereas in contrast, if the quantity exceeds 30% by weight, a mixinglayer tends to form between the coating and the photoresist pattern,which is undesirable.

The coating formation agent is preferably used in the form of an aqueoussolution with a concentration of 3 to 50% by weight, and even morepreferably from 5 to 20% by weight. If the concentration is less than 3%by weight, a satisfactory coating may not be formed on the substrate,whereas at concentrations exceeding 50% by weight, not only doesincreasing the concentration not produce an equivalent improvement inthe desired effects, but the handling of the agent also becomes moredifficult.

As described above, the coating formation agent is usually used in theform of an aqueous solution using water as the solvent, although a mixedsolvent of water and an alcohol based solvent could also be used.Examples of this alcohol based solvent include monovalent alcohols suchas methyl alcohol, ethyl alcohol, propyl alcohol, and isopropyl alcohol.The alcohol based solvent is added to the water in quantities of no morethan 30% by weight.

EXAMPLES

As follows is a more detailed description of the present invention basedon a series of examples, although the present invention is in no wayrestricted to the examples presented below. Unless otherwise stated,quantities refer to weight % values.

Example 1

0.1 mol of a compound represented by a formula 22 shown below, 0.08 molof the norbornane lactone acrylate of the formula 9, and 0.02 mol of acompound represented by a formula 23 shown below were dissolved in 500ml of methyl ethyl ketone (MEK), and 0.1 mol of AIBN was then added tothe solution and dissolved. The thus obtained solution was heated to atemperature of 65 to 70° C., and this temperature was maintained for 3hours. Subsequently, the reaction solution was poured into 3 L ofvigorously stirred isopropanol, and the precipitated solid was isolatedby filtration. The thus obtained solid product was dissolved in 300 mlof MEK, poured into 3 L of vigorously stirred methanol, and once againthe precipitated solid was isolated by filtration and then dried, andyielded a resin A (the component (A)) for which the weight averagemolecular weight (Mw)=6,000, Mw/(number average molecular weight(Mn))=2.0, and Tg=130° C.

To 100 parts by weight of the thus obtained resin A were added 3.0 partsby weight of triphenylsulfonium nonafluorobutanesulfonate (the component(B)), 1.5 parts by weight of triethanolamine, and 750 parts by weight ofa mixed solvent of PGMEA:EL (6:4), and following dissolution, thesolution was filtered through a filter of pore size 0.45 μm, therebycompleting preparation of a positive resist composition.

The thus obtained positive resist composition was applied to a siliconwafer using a spinner, and was then prebaked and dried on a hotplate at115° C. for 90 seconds, thereby forming a resist layer with a filmthickness of 300 nm.

This layer was then selectively irradiated with an ArF excimer laser(193 nm) through a mask pattern, using an ArF exposure apparatusNSR-S302 (manufactured by Nikon Corporation; NA (numericalaperture)=0.60; σ=0.75).

The resist was then subjected to PEB treatment at 115° C. for 90seconds, subsequently subjected to puddle development for 30 seconds at23° C. in a 2.38% by weight aqueous solution of tetramethylammoniumhydroxide, and was then washed for 20 seconds with water, and dried.

As a result of this photoresist pattern formation process, a holepattern (including a 1:1 dense pattern and a 1:3 isolated pattern) witha hole diameter of 140 nm was formed.

Next, a water soluble resin coating with a total solid fractionconcentration of 8.0% by weight, which was formed by dissolving 10 g ofa copolymer of acrylic acid and vinylpyrrolidone (acrylicacid:vinylpyrrolidone=2:1 (weight ratio)), and 0.02 g of “SurfadoneLP100” (manufactured by ISP Co., Ltd.) as an N-alkylpyrrolidone basedsurfactant in pure water, was applied to the surface of the hole patternto form a layered product. The film thickness (the height from thesurface of the substrate) of the water soluble resin coating of thelayered product was 200 nm. The layered product was then subjected toheat treatment for 60 seconds at a temperature of 110° C., 120° C., 130°C., or 140° C. Subsequently, the water soluble resin coating was removedby washing with pure water at 23° C.

FIG. 1 shows the hole diameter values for the hole pattern prior to heattreatment, and following heat treatment at each of the differenttemperatures. FIG. 1A shows the results for the dense pattern, and FIG.1B the results for the isolated pattern. The vertical axis of the graphshows the hole diameter (nm) of the produced hole pattern, and thehorizontal axis shows the exposure dose (mJ/cm²).

The results indicate that all of the plurality of hole patternsdisplayed a good shape with favorable retention of the vertical shapeobserved prior to the heat treatment. Furthermore, between 110° C. and130° C., there was very little variation in the degree of narrowingregardless of the temperature, and the hole diameter reduced bysubstantially 20 nm from the value prior to the heat treatmentFurthermore, differences in the exposure dose or the pitch also causedalmost no difference in the degree of narrowing.

Comparative Example 1

With the exception of replacing the resin A from the example 1 with aresin A′ comprising 2-ethyl-2-adamantyl acrylate/norbornane lactoneacrylate/3-hydroxy-1-adamantyl methacrylate in a ratio of 40/40/20(Mw=10,000, Mw/Mn=2.0, Tg=140° C.), and conducting the heat treatment ateither 140° C. or 150° C., a resist pattern was formed in the samemanner as the example 1.

FIG. 2 shows the hole diameter values for the hole pattern prior to heattreatment, and following heat treatment at each of the temperatures.FIG. 2A shows the results for the dense pattern, and FIG. 2B the resultsfor the isolated pattern.

The results indicate that all of the plurality of hole patternsdisplayed a good shape with favorable retention of the vertical shapeobserved prior to the heat treatment. However, there was considerablevariation in the degree of narrowing, with some hole diameters remainingunchanged, and others narrowing by 80 nm or more. Furthermore,differences in the exposure dose or the pitch also caused largedifferences in the degree of narrowing, and even comparing values at thesame temperature and the same exposure dose, the isolated patterndisplayed a larger degree of narrowing than the dense pattern.

INDUSTRIAL APPLICABILITY

According to the present invention, a resist pattern with minimalpattern variation within the plane of the substrate, and excellentuniformity can be formed with good control of the pattern size, which isindustrially very useful.

1. A method of forming a resist pattern comprising: a resist patternformation step, in which a positive resist composition comprising aresin component (A) that displays increased alkali solubility underaction of acid, and an acid generator component (B) that generates acidon exposure is applied to a substrate, a prebake is conducted, saidresist composition is selectively exposed, post exposure baking (PEB) isconducted, and alkali developing is used to form a resist pattern; and anarrowing step in which a pattern size of said resist pattern isnarrowed by heat treatment, wherein said component (A) utilizes a resinwith a structural unit (a1) derived from a (meth)acrylate esterrepresented by a general formula (I) shown below:

wherein, R represents a hydrogen atom or a methyl group; X represents ahydrocarbon group with 1 to 4 rings; R¹ to R³ either each represent,independently, a lower alkyl group, or alternatively, one of R¹ to R³represents a lower alkyl group, and two remaining groups represent loweralkylene groups, terminals of which are bonded together to form a singlering containing 5 or 6 carbon atoms including bonded terminal carbonatoms.
 2. A method of forming a resist pattern according to claim 1,wherein said component (A) utilizes a resin with a structural unit (a1)in which said groups R¹ to R³ each represent, independently, a loweralkyl group.
 3. A method of forming a resist pattern according to claim2, wherein said component (A) utilizes a resin with a structural unit(a1) in which said lower alkyl groups are either methyl groups or ethylgroups.
 4. A method of forming a resist pattern according to claim 1,wherein said component (A) utilizes a resin further comprising astructural unit (a2) derived from a (meth)acrylate ester with a lactoneunit.
 5. A method of forming a resist pattern according to claim 1,wherein said component (B) utilizes an onium salt with a fluorinatedalkylsulfonate ion as an anion.
 6. A method of forming a resist patternaccording to claim 1, wherein said positive resist composition furthercomprises a secondary or a tertiary lower aliphatic amine.
 7. A methodof forming a resist pattern according to claim 1, wherein said narrowingstep is a thermal flow process in which said resist pattern is heatedand softened, and a pattern size of said resist pattern is narrowed. 8.A method of forming a resist pattern according to claim 7, wherein saidpositive resist composition further comprises a compound with at leasttwo vinyl ether groups, which reacts with said resin component (A) onheating and forms cross linking.
 9. A method of forming a resist patternaccording to claim 1, wherein said narrowing step is a shrink process,in which a water soluble resin coating comprising a water solublepolymer is provided on top of said resist pattern, and subsequentlyheated, causing said water soluble resin coating to shrink, therebynarrowing a spacing of said resist pattern.
 10. A method of forming aresist pattern according to claim 9, wherein said water soluble polymerutilizes a polymer comprising a structural unit derived from at leastone monomer which acts as a proton donor, and a structural unit derivedfrom at least one monomer which acts as a proton acceptor.
 11. A methodof forming a resist pattern according to claim 10, wherein said watersoluble polymer is at least one polymer selected from a group consistingof acrylic based polymers, vinyl based polymers, cellulose basedderivatives, alkylene glycol based polymers, urea based polymers,melamine based polymers, epoxy based polymers, and amide based polymers.12. A method of forming a resist pattern according to claim 9, whereinsaid water soluble resin coating further comprises a water soluble amineandlor a surfactant.
 13. A positive resist composition for use within amethod of forming a resist pattern according to claim 1, comprising aresin component (A) that displays increased alkali solubility underaction of acid, and an acid generator component (B) that generates acidon exposure, wherein said component (A) is a resin with a structuralunit (a1) derived from a (meth)acrylate ester represented by a generalformula (I) shown below:

wherein, R represents a hydrogen atom or a methyl group; X represents ahydrocarbon group with 1 to 4 rings; R¹ to R³ either each represent,independently, a lower alkyl group, or alternatively, one of R¹ to R³represents a lower alkyl group, and two remaining groups represent loweralkylene groups, terminals of which are bonded together to form a singlering containing 5 or 6 carbon atoms including bonded terminal carbonatoms.
 14. A layered product in which a resist layer formed from apositive resist composition according to claim 13, and a water solubleresin coating comprising a water soluble polymer on the resist layer arelayered onto a substrate.
 15. A positive resist composition comprising aresin component (A) capable of displaying increased alkali solubilityunder action of acid, and an acid generator component (B) capable ofgenerating acid on exposure, wherein the resin component (A) contains aresin having a structural unit (a1) derived from a (meth)acrylate esterof general formula (I):

wherein, R represents a hydrogen atom or a methyl group; X represents ahydrocarbon group with 1 to 4 rings; R¹ to R³ either each represent,independently, a lower alkyl group, or alternatively, one of R¹ to R³represents a lower alkyl group, and two remaining groups represent loweralkylene groups, terminals of which are bonded together to form a singlering containing 5 or 6 carbon atoms including bonded terminal carbonatoms.
 16. A method of forming a resist pattern comprising: applying thepositive resist composition of claim 15 to a substrate; conductingpre-baking of the substrate with the positive resist composition;selectively exposing the resist composition; conducting post exposurebaking of the substrate with the selectively exposed resist composition;and forming by alkali developing a resist pattern using the postexposure baked resist composition; and narrowing a pattern size of theresist pattern by heat treatment.